1. Field of the Invention
This invention pertains generally to imaging systems and methods and more particularly to a laser engraving system and method in which an image of an object is formed on an output medium by a scanning laser beam.
2. Description of the Prior Art
Images formed by a scanning laser beam have a tendency to grow in the direction of beam travel. This inability to reproduce images from a paste-up on a 1:1 dimensional basis at the necessary exposure level has created significant problems, such as a muddiness or lack of contrast in halftone images reproduced by this method and growth in size of the text images. Because of this growth, it is generally necessary to employ a relatively high threshold setting in order to keep halftone shadows open. When the threshold is set high enough for this purpose, a characteristic breaking occurs in the top and bottom portions of letters such as C, O, and S.
In the past, there have been attempts to overcome the problem of imaging growth by techniques such as the use of special amplifiers and astigmatic optics, underexposure of the image, and the use of high gamma plates and strong developers. Utilizing such techniques, it is sometimes possible to reproduce images with the desired 1:1 relationship. However, these techniques are not suitable for use on anything but an individual basis.
It has also generally been necessary to expose halftones at a different camera setting than is normally used, and any type reproduced with the halftones shows growth for positively exposed plates and shrinkage for negatively exposed film systems.